The proposed research in the treatment of children with acute lymphocytic leukemia has the following objectives: 1) To determine in a controlled manner the relative efficacy and toxicity of two therapeutic regimens given early in remission for prophylaxis of central nervous system leukemia; 2) To determine the efficacy and toxicity of periodic "reinforcement" or "reinduction" chemotherapy in prolonging continuous complete remission; 3) To prolong the duration of leukemia- free survival with combination chemotherapy and preventive central nervous system therapy; 4) To analyze results in this to earlier studies to determine the reasons for differences, despite no apparent differences in therapy; 5) To continue studies of surviving patients for an indefinite period of time to detect late toxic effects of therapy such as growth impairment, the emergence of secondary neoplasms and gonadal dysfunction.